Conventionally, a so-called three-dimensional (3-D) image display apparatus is available that enables stereovision by the naked eye. There are a variety of schemes for the 3-D image display. For example, Japanese Patent Laid-Open No. 9-311294 discloses a rear-cross-lenticular scheme apparatus. FIG. 5 is a substantial-part perspective view showing an example of the rear-cross-lenticular 3-D image display apparatus. In FIG. 5, reference number 6 indicates a display device for displaying images, which may be a liquid-crystal display (LCD), for example. In this drawing, a polarizer, color filter, electrode, black matrix, and anti-reflection film, which are generally used in the liquid-crystal display, are omitted.
Reference number 10 indicates a backlight (surface light source). A mask substrate (mask) 7 having checkered openings 8 is provided between a display device 6 and the backlight 10. The mask pattern is provided by patterning deposited metal film such as chromium film or a light absorbent material on the mask substrate 7 made of glass or resin. The backlight 10 and mask substrate 7 form the light source for the 3-D image display apparatus.
Provided between the mask substrate 7 and the display device 6 are a first lenticular lens 3 and a second lenticular lens 4 made of transparent resin, glass, or other material. The first lenticular lens 3 is a longitudinal cylindrical lens array in which vertically elongated cylindrical lenses are arranged in the horizontal direction of the display. The second lenticular lens 4 is lateral cylindrical lens array in which horizontally elongated cylindrical lenses are arranged in the vertical direction of the display.
An image displayed on the display device 6 consists of a large number of horizontal stripe images L1 . . . n, R1 . . . n (where n is a predetermined natural number) formed by vertically dividing each of the entire right and left parallax images (not shown). These stripe images are alternately arranged in a manner, L1R1L2R2L3R3 . . . LnRn from top to bottom, for example, and displayed on the same display screen of the display device 6.
Light from the backlight 10 passes through the openings 8 in the mask pattern formed on the mask substrate 7 to illuminate the display device 6 and the right and left stripe pixels L, R are observed by the eyes of an observer.
That is, the mask substrate 7 is illuminated by the backlight 10 and the light is projected through the openings 8 of the mask pattern. Each of the cylindrical lenses making up of the first lenticular lens 3 positioned on the observer's side of the mask substrate 7 has such a lens curvature that its focal point is substantially on the mask substrate 7. Because the second lenticular lens 4 has no optical effects on the cross-section of the first lenticular lens, a beam of light projected through one opening 8 is transformed into a substantially parallel light beam in the first lenticular lens.
The width of openings 8 and light shielding portions in the mask pattern 7 is chosen so that a pair of the opening 8 and light shielding portion is equivalent to one pitch (the center distance between adjacent cylindrical lenses).
It can be ensured that the light from the openings 8 across the screen converges on the left or right eye by determining the pitch of the first lenticular lens 3 and the pitch of the pair of the opening and light shielding portion of the mask pattern based on the relation between the optical distance from the observer to the first lenticular lens 3 and the optical distance from the first lenticular lens 3 to the mask pattern 7. In this way, the left and right stripe images L1 . . . n, R1 . . . n on the display device 6 are observed in a manner that they are horizontally separated into areas for the left and right eyes.
The second lenticular lens 4 converges all the light beams traveling through the openings 8 of the mask pattern 7 on the stripe images on the display device 6 for the right of left eye to illuminate and transmit it and diverge them only in the vertical direction according to the NA (numerical aperture) at the time of the conversion, thereby providing an observation area where the left and right stripe pixels from top to bottom of the screen are equally and separately seen from a given eye-level of the observer.
However, the stereoscopic view angle of the 3-D image display apparatus is narrow and the 3-D image cannot be recognized when the viewpoint of the observer is out of the stereoscopic view angle. A technology is proposed that detects viewpoint of the observer (subject) and controls the 3-D image display apparatus in response to the movement of the viewpoint, thereby apparently enlarging the stereoscopic view angle. For example, Japanese Patent Laid-Open No. 10-232367 discloses a technology that moves a mask pattern or lenticular lens in parallel to a display surface to enlarge the stereoscopic view angle.
FIG. 6 shows the 3-D image display apparatus disclosed in Japanese Patent Laid-Open No. 10-232367. In FIG. 6, the same reference numbers are applied to the same components as those in FIG. 5 and the description of which will be omitted. The 3-D image display apparatus in FIG. 6 has only a lenticular lens which is equivalent to the first lenticular lens shown in FIG. 5, and does not have a lenticular lens 4 equivalent to the second lenticular lens 4 in FIG. 5.
In the 3-D image display apparatus configured in this way, a view angle control in response to the (horizontal) movement of an observer 54 is performed as follows. First, a position sensor 51 detects a horizontal displacement of the observer 54 from a predetermined reference position and sends information about the displacement to a control unit 512. The control unit 52 sends an image control signal to a display drive circuit 50 according to the displacement information. The display drive circuit 50 causes a first or second horizontal stripe image to be displayed on a display 6. The control unit 52 also generates an actuator drive signal based on the displacement information to drive an actuator 53, which moves a mask pattern 7 horizontally, to move the mask pattern 7 to a position where the observer 54 can best separate left and right stripe images. As a result, the coverage in which stereovision can be achieved is extended.
Japanese Patent Laid-Open No. 10-78563 discloses a method for performing a view angle control that follows the back-and-forth and side-to-side movement of an observer by forming a mask pattern 7 on a liquid-crystal display (LCD), for example, and forming openings and light shielding portions by display presentation to allow the pitch of the openings and light shielding portion to be changed dynamically.
In this case, the viewpoint position of the observer in side-to-side direction and back-and-forth direction must be detected. To determine the position, a method using stereo-vision can be used. Stereo-vision is a known object position determination method in which segment matching (a process of determining correspondence between segments (areas) based on the features of the areas) between a plurality of images captured by a stereocamera is performed to identify a three-dimensional position based on the triangulation principle according to a displacement of corresponding areas between the images.
Although this method extends the area in which stereovision can be achieved (the stereovision observation area) by detecting and following the viewpoint of the observer to more the stereovision observation area, the size of the stereovision observation area itself is fixed and the detection process of the viewpoint involves a delay, therefore the viewpoint may go out of the stereovision observation area if the observer moves fast. When the observer goes out of the stereovision observation area, a proper 3-D image cannot be observed. Therefore, there has been a need for a faster detection process for detecting the viewpoint of the observer observing the 3-D image display apparatus.